1. Field of the Invention
This invention relates to the field of telephone call and voice processing systems. More particularly it relates to a telephone voice mail and telephone call processing system adapted for use with a telephone key system.
2. The Prior Art
Multi-line customer telephone equipment is located at a telephone customer's place of business. Such equipment generally falls into one of two categories: PBX (Private Branch Exchange) or Key system. A PBX system in its simplest form simply routes 2-wire telephone connections among a number of standard 2-wire telephones. A telephone key system such as the Merlin.TM. and Merlin Plus.TM. available from the AT&T Corporation consist of a number of digital feature telephones in communication with a key system control unit ("KSU"). Digital communication paths between the digital feature telephones and the KSU provide information to the telephone regarding the status of the various telephone lines and extensions in the system. Separate audio communication paths (typically two per telephone) permit a telephone call and an intercom call to occur simultaneously at a digital feature telephone.
Voice mail systems are well known in the art. Such systems permit a number of users to share what is, in effect, a large random access telephone answering machine. Voice mail systems are difficult to implement for use with telephone key systems for a number of reasons. First, digital feature telephones generally do not generate audio DTMF tones when the number buttons (0-9, *, #) are pushed. Rather, key presses generate digital signals which travel over the digital signal paths--not the audio signal paths--to the KSU where they are processed and acted upon. If necessary, as in a telephone call, the KSU will translate the digital signals into audio DTMF tones and insert them on the audio of the outgoing telephone lines. Most voice mail systems are controlled by DTMF tones because DTMF tones provide the most practical approach to the control of voice mail systems, because they are commonly available on most telephones including public telephones.
Another difficulty with installing a voice mail system on a telephone key system relates to getting information on the status of the telephone lines and extensions as well as telephone audio into the KSU. Some voice mail systems (see, e.g., Ladd et al., U.S. Pat. No. 4,926,462) utilize a technique known as feature phone emulation. Ladd et al. uses a digital information connection between the voice mail system and a proprietary digital feature telephone port on a PBX to obtain call information regarding the ongoing call. No provision is made for obtaining information regarding other ongoing calls, nor is the voice connection made through the same emulated port. As a result, Ladd et al. utilizes a single emulated port together with a plurality of non-digital 2-wire ports to effect connections between a PBX telephone system and a voice mail system. Because it is relatively expensive to provide these non-digital 2-wire ports on a telephone key system, it is desirable to provide a telephone call and voice processing system which can be interfaced to a KSU directly through the proprietary digital feature telephone ports available on such systems.